Cascade developing apparatus



May 2, 1967 Filed Dec.

P. T. FERRARI ET AL CASCADE DEVELOPING APPARATUS 3 Sheets-Sheet 1 INVENTORS PATRICK T. FERRARI FRANKLIN S. REESE JOSEPH B. STONE A TORNE S May 2, 1967 T FE R R] ET AL 3,316,878

CASCADE DEVELOPING APPARATUS 3 Sheets-Sheet 2 Filed Dec. 30, 1965 May 2, 1967 P. T. FERRARI ET AL 3,316,878

CASCADE DEVELOPING APPARATUS Filed Dec. 30, 1965 3 Sheets-Sheet 5 FIG. 4

INVENTORS PATRICK T. FERRARI FRANKLIN smzasz BY 8.10551: 5. TONE M TORN rs United States Patent 3,316,378 CASCADE DEVELGPING APPARATUS Patrick T. Ferrari, Rochester, Franklin S. Reese, Victor, and Joseph B. Stone, Penfield, N.Y., assignors to Xerox gorporation, Rochester, N.Y., a corporation of New ror Filed Dec. 30, 1965, Ser. No. 517,599 6 Claims. (iii. 118--637) This invention relates to xerographic development apparatus and, in particular, to apparatus for developing both line and tone xerographic images each with different developer material.

More specifically, the invention relates to a xerographic developing apparatus adapted to contain two different developer materials, one for use in developing line copy and one for use in developing tone copy. In the art of xerography electrostatic latent images are produced on a photoconductive surface in accordance with a light image of the original copy being reproduced. The electrostatic images are developed to visible images with a pigmented resinous powder referred to herein as toner. The toner is brought into contact with the photoconductive surface and the electrostatic charge thereon attracts the toner material and causes it to adhere to the photoconductive surface in image configuration.

A method commonly used to bring the toner material into contact with the photoconductive surface is referred to as cascade development. In cascade development a carrier material consisting of glass or sand beads coated with a resinous material is mixed with the toner to provide mechanical control for the toner. The mixture of carrier and toner is referred to herein as developer. In cascade development the developer material is agitated to produce contact between the carrier and the toner and create a triboelectric charge which causes the toner to adhere to the surface of the carrier beads. The developer is then cascaded over the surface of a xerographic plate and toner particles on the carrier beads are attracted to the electrostatic latent image. Carrier beads and excess toner are returned to a sump where they are further agitated with additional toner and again recycled through the cascade process.

In the development of line copy, that is copy which does not contain continuous tone or half-tone images, the developer material is merely cascaded over the surface of the plate and the electrostatic image is such that the toner will be attracted to the image areas. However, in the development of continuous tone or half-tone images or the development of large solid areas a development electrode is used to intensify the electrostatic charge so that it will attract the toner material uniformly in proportion to the charge density.

A development electrode consists of a grounded or an electrically biased conductive surface placed in close proximity to the photoconductive surface. The development electrode increases the intensity of the electrostatic charge in image areas and increases the ability of the charge to retain toner.

When a development electrode is used during development the carrier may be of a size smaller than that used for line development so that the developer material will pass freely between the development electrode and the xerographic surface. Also the toner concentration may vary for the developer used for tone or line copy. In xerographic machines which are designed to operate on both line and tone copy, an electrode plate is positioned to be moved into and out of operative relationship with the xerographic plate. It is necessary, however, when switching from line copy to tone copy to completely switch the charge of developer material used in the development apparatus. This process is ditficult, dirty and 3,316,878 Patented May 2, 1967 time consu ming. It is therefore the primary object of this invention to improve xerographic apparatus to accornmodate two separate charges of developer material.

It is also an object of this invention to improve xerographic developing apparatus to permit line and tone copy to be developed in the same apparatus with different developer charges without removing or replacing the developer charge in the apparatus.

It is a further object of this invention to improve xerographic developing apparatus so that two different developer materials may be cascaded over the surface of a xerographic plate from the same angle.

These and other objects of this invention are attained by means of developer pods or containers which contain different developer material and which may be alternately operated to permit developer material from one pod to cascade over the surface of a xerographic plate while the developer material in the other pod is retained.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIG. 1 is a sectional side view of a xerographic developing apparatus incorporating one embodiment of this lnventlon.

FIG. 2 is a schematic side sectional view of the xerographic developing apparatus of FIG. 1 in a position wherein the developer from one pod is cascading over the plate. FIG. 3 is a schematic representation of a side sectional view of a xerographic developing apparatus of FIG. 1 in a position wherein developer from the other pod is cascading over the plate.

FIG. 4 is a partial front view of the apparatus shown in FIG. 1 with portions broken away to show internal structure.

FIG. 5 is a partial sectional view of a 'xerographic developing apparatus showing an alternate embodiment of the developer container.

Referring to the drawings, there is seen in FIGURE 1 a xerographic developer apparatus of a type suitable for use in an automatic xerographic camera of the type generally disclosed in copending application S.N. 348,- 950, filed Mar. 3, 1964, now Patent No. 3,272,101, and entitled, Xerographic Apparatus. The developer mechanism consists of a housing 2 supported from a bracket 4 which is rotatably mounted on a shaft 6. The housing 2 is secured to the bracket 4 by pins 8 and the bracket 4 can be rotated about the shaft 6 so that the housing 2 is inverted to the positions shown in FIGS. 2 and 3.

The housing 2 is an enclosed container having an opening generally indicated as it) over which a xerographic plate 12 may be secured by a clamp 14. The clamp 14 urges the plate 12 against a resilient gasket member 16 extending around the outside of the opening 10 to seal the opening and prevent spillage of developer material.

The xerographic plate 12 consists of a conductive base coated with a photoconductive layer. Prior to the insertion the photoconductive layer of the xerographic plate is charged uniformly with an electrostatic charge and exposed to a light image of copy to be reproduced. With the plate 12 in position to be developed, as shown in FIG. 1, a development electrode 18 is positioned closely adjacent to the surface of the plate 12. The development electrode 18 is supported on a pair of shafts 20 by brackets 22 and is movable towards and away from the surface of the xerographic plate 12 by a mechanism not shown. The elec trode is moved away from the surface of the plate 12 when line copy, that is, copy consisting primarily of printed material, rather than large solid areas or photographs, is

3 to be reproduced and is moved towards the surface of the plate 12 when copy containing continuous tone or halftone images or solid areas is to be reproduced. The electrode 18 has a pair of flared guides 24 which extend outward and back from the front surface of the electrode for the purpose of directing developer material over the surface of the xerographic plate.

At the bottom of the developer housing 2 there is located a two-compartment developer pod indicated generally as 26. The developer pod contains a developer material 28 which consists of a pigmented resinous powder and a glass or sand carrier bead coated with a resinous material. The toner or powder is attracted to and held on the surface of the carrier material by triboelectric attraction; the toner is carried across the surface of the xerographic plate 12 by the carrier material when the developer housing 2 is inverted to the position shown in FIGS. 2 and 3. The normal size of the carrier particles used in developing line copy is 600-750 microns in diameter, and in developing tone copy 250 microns in diameter. The smaller carrier size permits the electrode plate 18 to be positioned closer to the surface of the xerographic plate 12 without interfering with the flow of developer material.

It has been found that a low potential conducting surface placed in close proximity to the surface containing the electrostatic image will increase the electric field of large uniformly charged areas and improve the development characteristics of the image. The electrode is usually connected to the metal or conductive substrate of the xerographic plate. Preferably the electrode is placed as close as possible or in contact with the xerographic plate, however, in order to be able to cascade the developer material over the surface of the xerographic plate the electrode must be spaced therefrom. By using the smaller 250 micron size carrier material the development electrode may be placed closely adjacent to the surface of the plate Without impeding fiow of developer. During the development of line copy, however, the electrode plate should be moved away from the surface of the xerographic plate so that background charges, that is, small electrostatic charges located in non-image areas, are not strengthened and developed by the close proximity of the development electrode. One of the inherent characteristics of a development elec trode is that background, toner deposited in non-image areas, is increased over development processes not utilizing development electrodes.

The pods 30 and 32, containing developer for use with tone and line copy respectively, are intended to be used separately and are, therefore, each capable of being entirely enclosed to prevent the developer material located therein from cascading over the surface of the xerographic plate. A separator wall 34 extends upward from the base of the housing 2 and supports a movable cover or flap 36. The bottom of the housing 2, which also is the bottom of the pods 30 and 32, consists of compartment doors 38 and 40. The doors 38 and 40 are used to empty the pods 30 and 32 and are secured in a closed position by latches 42 and 44. The pods 30 and 32 are filled with developer through the plate opening 10. The pod cover 36 is pivotally mounted on a shaft 46 and extends the full length of the pods 30 and 32. Operation of the cover 36 is best seen in FIG. 4 wherein a handle 48 is mounted on a stub shaft 50 journaled in the side wall 52 of the housing 2 and secured to the shaft 46 by means of a pin 54. Movement of the arm 48 rotates the shaft 50 and the shaft 46 to move the cover 36 to either of the positions shown in FIG. 1. A tension spring 56 biases the handle 48 towards the closed position of the cover 36 in both positions. With the cover 36 in the position shown by the solid lines in FIG. 1, that is covering pod 30, the top of the cover 36 engages and cooperates with an elevated strip 58 in the side walls of the housing 2 to provide a seal for the developer 28. With the cover 36 moved to the position indicated by the dotted lines in FIG. 1, the contour of the cover is such that contact with the side walls of the housing 2 also provides a seal for the developer 28 in the pod 32. In this position the back of the pod, indicated by numeral 60, provides a smooth surface over which the developer in pod 30 may flow as it is being cascaded over the surface of the xerographic plate.

FIGURES 2 and 3 show the flow of developer material from each of the pods 32 and 30 respectively. As seen in FIG. 2, as the housing 2 is rotated so that the pod 32 is elevated above the plate 12, the developer material 28 cascades out of the pod 32, and is deflected by the guide 24 across the surface of the xerographic plate 12. At the lower end of the housing 2 the developer accumulates in a receiver pod 62 in a position to be cascaded back across the surface of the xerographic plate to the pod 32 when the housing 2 is rotated to a position wherein the pod 62 is elevated above the surface of the xerographic plate 12. In FIG. 3 the developer material 28 is cascading out of the pod 30 over the surface of the cover 36 down across the surface of the plate 12 to the pod 62. Again, when the housing 2 is rotated to the position wherein the pod 62 is above the surface of the xerographic plate 12, the developer material will be deflected by the guide 24 across the surface of the plate 12, back over the surface 60 of the cover 36 to the developer pod 30. The flowing action of the developer material across the surface of the xerographic plate produces development of electrostatic images on the plate surface.

The various parameters involved in the development of electrostatic images are all critical and very often affect the degree of development accomplished. For example, the angle at which the developer material is cascaded across the surface of the xerographic plate is important to the quality of the image developed. Likewise, the angle at which the developer material approaches the surface of the xerographic plate is also critical. An embodiment of the present invention which permits the developer material 28 to approach the xerographic plate from the same angle is seen in FIG. 5. In this embodiment, the developer material 28 is contained in a cylindrical container 66. A partition member 68 extends radially outward from a shaft 70 to divide the container 66 into two compartments 72 and 74. The shaft 70 may be rotated by the handle in the same manner as the shaft 46 shown in FIG. 4. However, in this embodiment there is no need for a biasing spring 56 since the partition member 68 presses against the sides of the housing 66 and prevents unintentional movement of the shaft 70. Rotation of the shaft 70 produces movement of the partition member 68 so that first one compartment is exposed to an opening 76 in the top of the container 66 and then the other compartment is exposed to the opening 76 while the first compartment is sealed off. In this manner the developer material from either compartment may be cascaded over the surface of the xerographic plate 12 while the developer material 28 in the other compartment is retained in the container 66. In either event, the developer material 28 leaves the container 66 through the same opening 76 and cascades down a surface 78 toward the xerographic plates so that the approach angle of the developer material is the same regardless of the compartment from which it originated.

With the housing returned to a vertical position, as shown in FIG. 1, and all the developer material returned to the particular developer pod from which it originated the xerographic plate 12 may be removed from the clamp 14. A new xerographic plate can then be placed on the clamp 14 and secured to the housing 2. This plate may have either line or tone copy and, depending on the type of copy to be reproduced, the development electrode will be positioned relative to the xerographic plate. The op erator may also select the type of toner desired by either flipping the cover 36, shown in the first embodiment, or by rotating the partition 63 of the second embodiment to accommodate the particular type of image on the plate 12.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

What is claimed is: 1. Apparatus for developing electrostatic images on a xerographic plate including a developer housing having its longitudinal axis extending vertically and an opening in one side of a size sufiicient to accommodate a xerographic plate,

clamping means positioned to hold a xerographic plate over the opening in the housing,

chamber means adjacent one end of the developer housing to contain two separated charges of developer material,

means to cascade each of the charges of developer material over the surface of the xerographic plate, said chamber means including a displaceable wall member arranged compatible with the flow path of the developer material to retain one charge of developer material while the other charge is being cascaded.

2. The apparatus of claim 1 wherein said chamber means to contain separate charges of developer material comprises two pods located at the bottom of the developer housing and having one surface open to the interior of the developer housing,

and said displaceable wall member means to retain each developer charge is mounted between the developer pods and movable from a first position enclosing one developer pod to a second position enclosing the other developer pod.

3. The apparatus of claim 1 wherein said chamber means to contain two developer charges comprises a substantially cylindrical hollow member in the bottom of the developer housing having an opening exposed to the interior of the developer housing, said displaceable wall member being mounted on an axis position in the center of said hollow member to define two compartments whereby the wall member seals off one portion of the hollow member while the other portion is exposed to the opening and upon rotation will expose the other portion of the hollow member to the opening while the first portion is sealed.

4. A developing apparatus for developing electrostatic latent images by selectively cascading developer material thereacross according to the electrical characteristics of the latent image comprising:

contiguous walls forming an enclosed longitudinally extending housing, a one of the longitudinally extending walls being formed with an opening therein to receive a xerographic plate having an electrostatic latent image formed thereon, said one wall being inclined outwardly adjacent the opening to define a trough with said xerographic plate for receiving developer material,

support means to suspend and mount said housing about an axis which is transverse with respect to its longitudinal extent and adapted to pivotally rock said housing to thereby cascade developer material, alternately back and forth, across the latent image;

a backing electrode extending parallel to said plate along substantially the length thereof and closely spaced thereto, said backing electrode carrying guide means at the ends thereof which are flared away from said plate to guide developer material into said trough and said electrode, including the guide means are adapted for movement toward and away from said plate according to the size of the developer material cascaded;

chamber means located at one end of said housing to separately contain two different developer materials associated with producing line and tone copy, said chamber means being in communication with the interior of said housing and including a displaceable wall movable to retain a one of said developer materials while permitting the other developer material to cascade across said latent image, said chamber means having an interior contour compatible with the flow path of the developer material; and settable means to position said displaceable wall according to the particular developer material utilized in the development of the electrostatic latent image.

5. Apparatus according to claim 4 wherein said chamber means comprises a pair of compartments having a common fixed wall bottom of the developer housing each compartment being in communication with the interior of the housing, said displaceable wall being pivot-ably mounted on said common wall and movable from a first position to close off a one of said compartments to a second position to close off the other.

6. Apparatus according to claim 4 wherein said chamber means comprises a member having a substantially cylindrically shaped recess exposed to the interior of the developer housing, said displaceable wall member being rotatably mounted on an axis positioned in the center of the recess to divide said member into adjoining compartments.

References Cited by the Examiner UNITED STATES PATENTS 956,942 5/1910 Clemmer 222-l42.6

982,371 1/1911 Lacy ZZZ-142.6 1,835,247 12/1931 Smagola 222-142.6 2,550,724 5/1951 Sabel et al 118-57 X 2,550,738 5/1951 Walkup 118-57 X 2,606,691 8/1952 Lindly ZZZ-142.6 X 3,160,057 12/1964 Murray et a1. 95-1.7 X

MORRIS KAPLAN, Primary Examiner. 

1. APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGES ON A XEROGRAPHIC PLATE INCLUDING A DEVELOPER HOUSING HAVING ITS LONGITUDINAL AXIS EXTENDING VERTICALLY AND AN OPENING IN ONE SIDE OF A SIZE SUFFICIENT TO ACCOMMODAWTE A XEROGRAPHIC PLATE, CLAMPING MEANS POSITIONED TO HOLD A XEROGRAPHIC PLATE OVER THE OPENING IN THE HOUSING, CHAMBER MEANS ADJACENT ONE END OF THE DEVELOPER HOUSING TO CONTAIN TWO SEPARATED CHARGES OF DEVELOPER MATERIAL, 